This invention is related to crimping machines for contracting the collar of a hose coupling onto a hose end and more particularly to the crimping dies of such machine.
In the crimped form of coupling essentially the entire collar of the hose coupling is engaged by the crimping equipment and reduced in diameter to secure the hose end between the couping collar and an insert member of the coupling. This is done typically in a single operational step, requiring only radially inward movement of the collar.
This form of crimping apparatus is well known and is described in some detail in U.S. Pat. No. 4,309,892. In this patent a hydraulic ram is used to drive a circular array of die segments toward the narrow end of a tapered bowl, causing a simultaneous radial inward movement of the die segments and a contraction of the die opening at the center of the array. With the collar of a hose coupling positioned within the die opening, radial inward deformation is effected to secure the coupling on the hose end.
Enormous forces are encountered in crimping machines of this type which, for example, for two inch diameter hose couplings, may require about 200 tons of force from the hydraulic ram to perform the crimping operation. In driving the die segments into the tapered bowl, the axial movement of the dies is converted into a radial contraction by the camming action of the wall of the bowl. In U.S. Pat. No. 4,309,892 the die segments are supported and spaced in a circular array prior to crimping, by a die separator. This is a tubular device with a serrated edge adapted to receive a complementary angled surface at the bottom of each die segment. The die separator is fitted at the narrow end of the bowl and is spring biased to move with the die segments during the crimping operation. Due to the great forces involved, however, the die separator provides little more than an initial locating and guiding of the segments. Once the hose collar is contacted by the die segments and radial deformation begun, continued circular spacing and linear motion of the die segments is dependent upon stability of the structures involved, distribution of forces, frictional effects, and the like. One device employed in the prior art to assure simultaneous movement of the die segments into the bowl, is a spacer ring which is disposed on the segments and which transmits force of the ram to all of the segments.
While prior art crimping machines can produce satisfactory crimped couplings, on occasion difficulties have been encountered which have resulted in less than satisfactory crimped hose ends. In the prior art structures the outer surface of the die segments is a conical surface generally matching the conical surface of the bowl in which it is disposed. However, since the die segments move axially with respect to the bowl there is only one location where a true match between the surfaces is obtained. In other locations, as would be expected at the intersection of conical surfaces of matching slope but different diameters, only a line of contact occurs. This results in a relatively unstable structure subject to the requirement that a great quantity of force must be transmitted through the relatively small surface area. In actual practice, some flattening of this line of contact occurs to accommodate these forces, however such deformations are not always predictable, nor do they result in much more stable structures.
What does occur is that the die segments move relatively unpredictably since they are not constrained entirely in their motion. Thus they may become angled within the bowl, either being cocked or rocked about their initial line of contact, with respect to their desired axial line of movement through the bowl. Under some conditions, to a limited extent, the line of movement of the die segments through the bowl may even be somewhat helical.
The instability of prior art structures could produce undesirable results. For example, galling or surface damage could occur to the die segment or to the bowl structure. With rocking of the die segments uneven contraction of the coupling collar could occur. In some instances a domino-like effect of cocked die segments produces a ratcheted or sprocket-like effect on the coupling collar. Since integrity of the coupling is dependent to a great extent upon concentricity of the crimped collar with respect to the hose and the insert of the coupling, uncertain results could be obtained.